Megatron-UK

Am I right in thinking that there are two cats in the Turbo 2 setup? One cat before the main exhaust box (is this the part that a cat-bypass replaces?) and a second smaller cat after the wastegate?

Which part part the 'swan neck' or 'G' pipe replace?

cobalt

Okay this is the info from the TSB I quoted a while back.

Found the TSB. Number 9032 9307.

Reads:

Concern: The boost gauge in 1994 911 Turbos will only read 0.7 bar at max boost

General Information The boost pressure for 1994 3.6 liter 911 turbos is .79 to .85 bar. 1994 911 Turbos are equipped with a boost gauge that is only capable of registering 0.7 bar. For technical reasons, the software for the boost pressure gauge was taken from the 3.3 liter 911 Turbo.

Should a 1994 3.6 Liter 911 Turbo have a customer complaint or "car will only reach 0.7 bar boost," the complaint must be verified and boost pressure must be checked before repairs are performed.

If boost pressure is within specifications, no repairs are necessary.

Repair Information: 1994 3.6 Liter Turbo Max boost 0.79 to 0.85 bar 1992 3.3 Liter Turbo Max boost 0.75 to 0.81 bar

Damage code 903210 0002


As you can see the cars leave the factory with over .75 bar and could be as high as .85 depending on the car. The factory numbers are what I was told to be a minimum requirement. So at minimum you will see 320 hp. Porsche has always been known to be conservative when stating Hp numbers.

If you changed the spring from stock to 1.0 bar without other mods you are not looking at a major gain in HP. The 1 bar works with other changes to increase hp.

I am running 1 bar spring which holds at 1 bar exactly a HF K27 B&B headers Swans neck and cat. I do not know what the car dynoed at before the changes but It was up to 390 without the 1 bar spring and when the spring was added and properly dyno tuned she is pumping out 430 hp. If I remove the cat it should be worth another 20 hp, reduce heat and bring on boost sooner although I am told that the cat helps keep overboost down. I am thinking of going with the 100 cell cat but at $1300+ expense I don't drive the car enough to warrant the expense.


Yes 2 cats. The large cat is just behind the license plate and the small cat just off the waste gate. The muffler is the large box on the right hand side of the engine the G pipe swans neck replaces this. I do not know who if anyone makes a swans neck for these cars. I had one custom fabricated. It makes for a better sound than the G pipe. Nice burble on lift off.

Y65MPH

Correct on the Cats. One primary attached to the turbo and the other attached to the wastegate.

The swan neck replaces the secondary muffler(the muffler is located next to the passenger rear wheel).

Craig

Megatron-UK

So, if you were to fit both a primary cat bypass (1991 cars will be exempt in the UK) and a swan neck/G-pipe, then am I right in thinking that the system will then be effectively straight through?

911addict

Magatron,
Yes, clear breathing!
The original muffler/silencer by Porsche is very freeflowing anyway, but is 'silenced'. The muffler bypass will not add HP but will change sound as Cobalt says. Many have previously said that both Cat and muffler bypass together is too loud for most. The g-pipe is known to be louder, cheaper and lighter than the swans neck (Swans neck made by Scart).
Hence my decision to fit 100cell cat (by Scart) for better breathing (response and power) and sound. If not loud enough will fit swans neck purely for sound.
Will also consider the turbo wastegate bypass pipe (again Scart make a nice looking one) purely for sound on boost, as JBL930 suggests. (The WG cat will not affect power, just sound).

All this info is based on what I have picked up from various discussions, mainly on Rennlist.

BTW, are we all agreed that a 1 bar spring will not make the boost more brutal, but will just rise further?

PS: Cobalt, several rennlisters swear that the 1bar spring alone makes a substantial power difference. Don't know if this is pure HP or torque?

Megatron-UK

Gotcha! I think it was mainly the US/UK terminology differences that had me confuddled about the exhaust system.

I'll probably be looking for a little more power and noise once I get myself a car, but don't think I could put up with a straight through system in day to day use (I've had cars with straight through systems in the past and though they sound good, they can get tiring after a while) - I'll probably just go with a cat-bypass myself.

cobalt

I don't think you will see more than a 20+ hp gain (5%) on the 3.6 by going with the 1.0bar spring the 3.3's get a bit more boost increase so they might see more hp. I guess this is substantial, I feel a 70 hp or 20% increase to be substantial and this can only be achieved by doing several mods together. So I guess it all depends on what you consider substantial.

I also find that increasing Hp is only part of the equation. applying boost earlier to give a better more useable power band makes the car much more streetable and enjoyable. You can achieve very high HP numbers and have a limited power band which might be fine for track use but doesn't make for a very enjoyable street car.

Megatron-UK

If the Porsche motor is anything like the other turbocharged engines I've tweaked before, then removing restrictions in the exhaust can often decrease the time / revs needed for the turbo to spool up - the cat is usually the biggest gain in that area.

I know where cobalt is coming from, with regards to big hp; I've got (well, did - it's now sold!) a little mk1 MR2 to which I've fitted a 2.0 turbo motor from the bigger mk2 - as standard it has a very quick spool-up from the a ceramic turbine in the stock turbocharger.
Now me being me I wasn't content with that, so I fitted a turbo with a larger compressor section from a mk3 Supra Of course instead of a decent amount of useable boost at 3500rpm, it only starting making noticeable power (>8psi) at around 4000rpm (full 16psi only after 4300rpm)... the power delivery was changed immensely - it became a very, very fast car indeed; faster than my stock mk4 supra TT, but it wasn't as easy to drive, nor as comfortable. Huge fun though

911addict

Cobalt,
so for USEABLE pwer (ie. low-mid) response, what mods do you put high on the list? Flywheel, exhaust, what else? Would you include boost spring?

cobalt

To me the best improvement after headers was the K27 Hf and 1 bar spring. My car actually feels more like a N/A car than a turbo car once in the revs. By adding the K27 HF the power can be feathered like a N/A car vs the on/off effect that the stock turbo gave you. I believe if I add the 100 cell cat it would reduce the initial lag that is still somewhat present when off boost and need quicker WOT response.

In my cars current state I am at full boost at 3200 rpms which is much better than it was stock. So long as a car is tuned properly I feel there is no problem with a 1.0 bar spring. If you feel less comfortable you can always try a .95 bar spring and add some safety zone.

I have heard both pros and cons to the light weight flywheel. That is also something I am thinking of doing eventually. It should make the engine rev much faster.

911addict

I'm really looking forward to my new Cat and of course will post results.

Also, I've said this before that my car seems to have a very smooth and strong power delivery and don't notice lag at all, even coming from NA 3.2's. I can only assume that the engine and turbo components are all in good order and marginally helped by the s/s heat exchangers.

Regarding lightened flywheel, the only experience I had was with my first car, a 1979 mini 1275GT and it really made a difference. At first it was difficult to pull away without screeching the tyres but soon got used to it and the response was greatly improved. Based on that when my clutch goes I'd like to try it on the turbo.

Deanriffs

Interesting...I test drove a '91 3.3T whose boost guage displayed 1.1 bar on boost. It must have been modded, based on what's being said is stock boost in this thread. The PPI didn't say that it was modded, but then I didn't ask.

cobalt

This was the digital illuminated gage in the tach? I have been trying to find a way to modify mine but have been told it is not possible.

Deanriffs

Yes, this was the digital gage in the tach. I almost wonder if it was malfunctioning, as the car appeared stock in pretty much all other respects.

Turbo Jonny

I have noticed on another thread that Imagine Auto and others have said removing the Lamda sensor is a good idea.It helps fuel economy in off-boost situations, so removing it would give quicker pick-up? Anyone illuminate the benefits as it is an easy mod for those of us just starting?